The present invention relates to a new and improved method and apparatus for measuring the length of a thread or the like withdrawn overhead from a spinning cop or a yarn bobbin wound on a spinning cop or a random crosswound bobbin. The invention equally relates to the use of the inventive method.
In the context of this disclosure the term "thread" is used in its broader sense to mean threads, yarns, and generally other types of filamentary materials.
The method can be used both for all pirns where the thread length of a winding layer or the thread length of two successive winding layers is constant. This is not the case for instance with so-called "precision windings". Prior to further processing the yarn, for instance present from the spinning machine in the form of a spinning cop, as a rule is rewound at another winding body, accommodated to the next following processing step, for instance into a cross-wound package, wherein during the course of the winding operation there is also brought about an improvement in the yarn quality, for instance through the use of a yarn clearer. If the formed wound bodies or packages are parallelly processed during the next following processing step, then irregular thread lengths upon these wound bodies lead to bothersome phenomena which retard the production, for instance, cause premature shutdown of the textile machine and increased work expenditure for preparing the winding residues.
Therefore, methods and apparatuses have already been proposed in the art in order to measure the length of the thread at the formed wound bodies, while striving to maintain as constant as possible the length for all the formed wound bodies.
For instance, a method is known from Swiss Pat. No. 588,067 wherein from the diameter of a cross-wound bobbin which is directly driven at its shaft and takes-up the payed-off thread and from the number of revolutions carried out by this cross-wound bobbin it is possible to determine the length of the wound-up thread through the use of an appreciable expenditure in electronic equipment. The computed value obtained according to this procedure is hardly satisfactory, because there is extensively not taken into consideration the correlation between diameter and winding density at the formed cross-wound package.
With other heretofore known devices, for instance as disclosed in Swiss Pat. No. 597,589 and Swiss Pat. No. 568,233, there is derived the length of the withdrawn thread from the number of revolutions of either the friction drum which drives the winding body to be wound at a constant circumferential speed or the withdrawl drum which withdraws the thread. This procedure does not take into account the unavoidable and irregular slip between the friction drum and the winding body or between the withdrawl drum and the withdrawn thread, so that the "measured length", as a general rule, is larger than the "true length" of the withdrawn thread.
Finally, with the equipment disclosed in Swiss Pat. No. 473,378 the withdrawn thread is frictionally driven by means of a measuring roll and predictated upon the number of revolutions of the measuring roll there is attempted to be determined the length of the thread which is drawn over the measuring roll. Also in this case there is not taken into account the unavoidable and irregular ship which arises between the thread and the measuring roll.